Influences of Final Processing Methods on Surface Physical Properties and Fatigue Life for Railway LZ50 Steel

Abstract

Different final processing methods can bring about the difference in physical properties of metal materials, such as micro-structures, surface hardness, and residual stress. It can in turn influence the anti-fatigue performance of material. To compare the effects of two commonly used final processing methods on the properties mentioned above, two groups of smooth round bar specimens of LZ50 axle steel were utilized. The final machining process for the first group is finish turning, and that for the second one is surface rolling. Layer-stripping test results reveal that much higher residual compressive stress is engendered in surface and sub-surface of the rolling specimen. The surface micro-hardness of the first group is also higher than that of the second one. Furthermore, the micro-structures of these two kinds of specimens are somewhat different in local regions. Stress controlled fatigue tests were performed. The average fatigue life of surface rolling specimens is more than six times the life of finish turning ones. So the former final processing method is more suitable for improving the performance of present material.